Maintenance Ruby 3.4 gets fixes, but no new features. Switch to Ruby 4.0 →
class method
Math.lgamma
(::Math::double x) -> [ ::Float, -1 | 1 ]
Math.lgamma(x) → [float, -1 or 1]
math.c
View on GitHub ↗
static VALUE
math_lgamma(VALUE unused_obj, VALUE x)
{
double d;
int sign=1;
VALUE v;
d = Get_Double(x);
/* check for domain error */
if (isinf(d)) {
if (signbit(d)) domain_error("lgamma");
return rb_assoc_new(DBL2NUM(HUGE_VAL), INT2FIX(1));
}
if (d == 0.0) {
VALUE vsign = signbit(d) ? INT2FIX(-1) : INT2FIX(+1);
return rb_assoc_new(DBL2NUM(HUGE_VAL), vsign);
}
v = DBL2NUM(lgamma_r(d, &sign));
return rb_assoc_new(v, INT2FIX(sign));
}
Returns a 2-element array equivalent to:
Example
[Math.log(Math.gamma(x).abs), Math.gamma(x) < 0 ? -1 : 1]
See logarithmic gamma function.
-
Domain:
(-INFINITY, INFINITY]. -
Rangeof first element:(-INFINITY, INFINITY]. -
Second element is -1 or 1.
Examples:
Example
lgamma(-4.0) # => [Infinity, -1] lgamma(-3.0) # => [Infinity, -1] lgamma(-2.0) # => [Infinity, -1] lgamma(-1.0) # => [Infinity, -1] lgamma(0.0) # => [Infinity, 1] lgamma(1.0) # => [0.0, 1] lgamma(2.0) # => [0.0, 1] lgamma(3.0) # => [0.6931471805599436, 1] lgamma(4.0) # => [1.7917594692280545, 1] lgamma(-2.5) # => [-0.05624371649767279, -1] lgamma(-1.5) # => [0.8600470153764797, 1] lgamma(-0.5) # => [1.265512123484647, -1] lgamma(0.5) # => [0.5723649429247004, 1] lgamma(1.5) # => [-0.12078223763524676, 1] lgamma(2.5) # => [0.2846828704729205, 1]
Related: Math.gamma.